On Fri, Jul 27, 2018 at 07:20:30AM +0200, Takashi Iwai wrote:
I think there is a mistake on the reported-by tag.
The reported-by tag (e4c8abb920ef...) is for WARNING in port_delete.
I guess the tag below is correct.
Reported-by: syzbot+619d9f40141d826b097e@xxxxxxxxxxxxxxxxxxxxxxxxx
Could you please make sure that the reported-by tag is correct?
By the way, I can't reproduce the crash WARNING in port_delete so
far. I feel sad for saying this..
I really want to reproduce the crash and thus, to help to fix the
crash. If there is any progress on it, I will let you know
immediately.
Best regards,
Dae R. Jeong
> On Fri, 27 Jul 2018 06:13:22 +0200,
> Dae R. Jeong wrote:
> >
> > I tested it and it worked.
> > Thanks a lot!
>
> Good to hear. Below is the final patch with a proper comment (and
> with syzbot reported-by, too) I'm going to queue to sound.git tree.
>
>
> thanks,
>
> Takashi
>
> -- 8< --
>
> From: Takashi Iwai <tiwai@xxxxxxx>
> Subject: [PATCH v2] ALSA: virmidi: Fix too long output trigger loop
>
> The virmidi output trigger tries to parse the all available bytes and
> process sequencer events as much as possible. In a normal situation,
> this is supposed to be relatively short, but a program may give a huge
> buffer and it'll take a long time in a single spin lock, which may
> eventually lead to a soft lockup.
>
> This patch simply adds a workaround, a cond_resched() call in the loop
> if applicable. A better solution would be to move the event processor
> into a work, but let's put a duct-tape quickly at first.
>
> Reported-and-tested-by: Dae R. Jeong <threeearcat@xxxxxxxxx>
> Reported-by: syzbot+e4c8abb920efa77bace9@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> ---
> sound/core/seq/seq_virmidi.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c
> index 289ae6bb81d9..8ebbca554e99 100644
> --- a/sound/core/seq/seq_virmidi.c
> +++ b/sound/core/seq/seq_virmidi.c
> @@ -163,6 +163,7 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream,
> int count, res;
> unsigned char buf[32], *pbuf;
> unsigned long flags;
> + bool check_resched = !in_atomic();
>
> if (up) {
> vmidi->trigger = 1;
> @@ -200,6 +201,15 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream,
> vmidi->event.type = SNDRV_SEQ_EVENT_NONE;
> }
> }
> + if (!check_resched)
> + continue;
> + /* do temporary unlock & cond_resched() for avoiding
> + * CPU soft lockup, which may happen via a write from
> + * a huge rawmidi buffer
> + */
> + spin_unlock_irqrestore(&substream->runtime->lock, flags);
> + cond_resched();
> + spin_lock_irqsave(&substream->runtime->lock, flags);
> }
> out:
> spin_unlock_irqrestore(&substream->runtime->lock, flags);
> --
> 2.18.0
>
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
